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moves deeper into the soil profile than would be expected from results obtained from models. Soil-derived dissolved organic matter (DOM) has been shown to This rapid, sometimes unpredictable transport of orform stable complexes with the herbicide napropamide [2-(-naphthoxy-N,N-diethylpropionamide] capable of enhancing the transport ganic chemicals in soil is most often attributed to preferof napropamide through soil columns. Two soils, one containing sew- ential flow pathways. Jury et al. (1986) found that about age sludge–derived organic matter (SS) and the other having only 20% of the total mass of napropamide and prometryn natural organic matter (NoSS) were treated with napropamide and [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] apallowed to dry to promote complex formation. Soil columns were plied to the soil surface moved beyond the depth where prepared by packing a 10-cm layer of untreated, dry, sieved soil fol- existing chemical transport models predicted they would lowed by an overlying 5-cm layer of napropamide-treated soil. Col- reach by mass flow and adsorption reactions. In addiumns were irrigated and the effluent collected and placed in dialysis tion, it was found that under both conservation and no chambers. After equilibration napropamide concentrations were detill management an average of 18.8, 9.4, and 10.4% of termined on both sides of the membrane and complex and quantified the recovered atrazine [2-chloro-4-(ethylamino)-6-(isobased on the amount of napropamide unable to cross the membrane. It was found that for the SS soil 7% and for the NoSS 2.4% of the propylamino)-s-triazine], prometryn, and napropamide, applied napropamide underwent facilitated transport. In addition, respectively, were found in the 30- to 150-cm depth layer most of the complex transported through the columns had a molecular while they were expected to be retained in the top 20 weight between 500 and 1000 Daltons (Da). The solutions from the cm (Ghodrati and Jury, 1992). A review by Flury (1996) SS soil were also found to have formed at least two distinct complexes of the experimental literature on pesticide transport in that were resolved after passing through the untreated soil layer. The field soils revealed that there is still a lack of knowledge results obtained were in agreement with other published results and about the mechanisms responsible for rapid chemical the techniques used offer a way to separate and concentrate DOM transport. Mechanisms such as soil-induced changes in complexes from column effluents for further characterization. the sorptive behavior of the pesticide, due to complexation with DOM, can also lead to increased transport of a small portion of applied compound through soil in

The herbicide napropamide [N,N-diethyl-2-(1-naphthyloxy)propanamide] has been shown to complex with various sources of dissolved organic matter (DOM), potentially increasing the risk of ground water contamination by facilitating napropamide transport through soil. Two factors that may reduce the threat of facilitated transport of chemicals through soils are soil profile depth and soil horizon variability. Movement through the soil profile may cause herbicide complexed with DOM to break apart and readsorb to the soil. Differences in soil horizon organic matter content throughout the soil profile may also alter the potential for facilitated transport of herbicides. Napropamide was used in column studies to determine if organic matter differences in horizons and soil profile depth would reduce the risk of facilitated transport. A silt loam soil was used with and without sewage sludge amendment (SS and NoSS) to represent differences in organic matter content. Results showed that

Napropamide [2-(α-naphthoxy)-N,N-diethyl propionamide] has been shown to form soluble complexes with dissolved organic matter (DOM). Batch equilibrium and soil column leaching studies were performed to evaluate the effect of a drying event following herbicide application on napropamide-DOM complex formation. Napropamide was applied directly to the soil and allowed to dry and compared with studies where the herbicide was not allowed to dry. In batch studies the presence of napropamide-DOM complexes was inferred from reduced sorption coefficients measured on extracts of treated soils as compared with those from aqueous solutions. In column studies, drying was shown to induce herbicide movement with the wetting front even when preferential flow pathways were eliminated. The formation of napropamide-DOM complexes was verified by dialysis tubing techniques. Increased napropamide movement through soil was the result of stable napropamide-DOM complexes that lacked an adsorption affinity. Although less than 6% of the total herbicide applied moved by facilitated transport, this amount of rapidly mobile pesticide could significantly increase the potential for ground water contamination. Results suggest that preventing the applied herbicide solution from drying before irrigation could reduce or eliminate the threat of facilitated transport of napropamide by DOM. We suggest that a short irrigation period after herbicide application could allow for herbicide movement beyond the soil surface to deter drying while preventing deep movement of pesticide with the water front.

Dissolved organic matter (DOM) has been shown to form a stable complex with Napropamide [2(α-naphthoxy)-N,N-diethyl propionamide] and to facilitate its transport through soil columns. Liquid-liquid extraction of organics is a common method to transfer napropamide from water into an organic phase for gas chromatography analysis. A study was conducted to determine the effect of Aldrich humic acid, soil-derived dissolved organic matter, electrical conductivity, and hydrogen ion activity on the ability of hexane to extract napropamide from solutions and from soil extracts. The electrical conductivity of Aldrich humic acid solutions (0.0, 48, and 100 mg C L -1 ) were adjusted to 0.01, 0.97, and 1.69 dS m -1 by adding NaCl and CaCl 2 , and pH (8.2, 7.4, and 5.6) was adjusted using HCl and NaOH. Electrical conductivity had no effect on extraction efficiency. In the absence of DOM pH had no effect on extraction efficiency. Extraction efficiency decreased with increasing DOM concentration. Maximum reduction in extraction efficiency occurred in the presence of DOM when solution pH was near neutrality. A maximum extraction efficiency of 100% was observed in the absence of DOM and a minimum of 68% when napropamide was added to DOM solutions at pH 8.2 and then lowered to pH 5.6. Management practices such as liming and allowing napropamide to dry on the soil may increase environmental transport. Also quantification of napropamide in environmental samples can be affected by DOM.

Equilibrium dialysis is commonly used to measure the complex formed between dissolved organic matter (DOM) and pesticides such as napropamide [2(α-naphthoxy)-N,N-diethyl propionamide]. Currently the dialysis method most often used employs dialysis tubing that is clamped on both ends. Limitations of the dialysis tubing method include difficulty in sample addition to the dialysis tubing, dilution effects, and the need for large sample volumes. A new dialysis chamber constructed of Teflon and using flat dialysis membranes is described and characterized using napropamide as a model compound. Using a dialysis membrane with a molecular weight cut off of 500 Daltons the system reached equilibrium across the membrane within 120 h. Significant sorption of napropamide to the membrane was observed. Napropamide sorption was linear, reversible, and dependant on the membrane used. Sample addition and removal from the chamber is possible without destroying the integrity of the membrane. The dialysis chamber allowed for fast and easy quantitative addition and removal of sample for dialysis without wasting sample. The small chamber made possible dialysis of very small samples (as little as 1.5 mL) while maintaining a large surface area for diffusion. The chamber also provided dialysis with a maximum dilution factor of two since the volume of dialysate needed is equal to the volume of sample introduced.

Organic matter amendments to soil are usually thought to improve soil quality. Increased soil organic matter can lead to increased concentrations of dissolved organic matter (DOM). Complexation of DOM with pesticides can lead to increased aqueous phase concentration and therefore enhanced movement through the soil profile. Dissolved organic matter has been shown to form a stable complex with napropamide [2(α-naphthoxy)-N,N-diethyl propionamide] and facilitate its transport through soil columns. Equilibrium dialysis is a common method to determine napropamide DOM complexation. Napropamide was applied to a silt loam soil with (SS) and without (NoSS) sewage sludge application. Solutions from batch equilibrium experiments were analyzed using equilibrium dialysis with various molecular weight cutoffs to determine napropamide DOM complexation. A maximum of 16% of solution phase napropamide was found to be associated with a DOM complex having a molecular weight >500 Daltons. The maximum complex size had a molecular weight

Phenanthrene, a 3-ring aromatic hydrocarbon, was used as a model substrate to analyze the effect of sorption on the bioavailability of polycyclic aromatic hydrocarbons (PAHs). This study focused on sorption to mineral-associated humic acid (HA). Batch sorption analyses of phenanthrene to mineral-HA complexes were performed as integral part of the bioavailability experiments to account for the sorbed fraction under the various experimental conditions. A mixed culture that was enriched from a coal tar contaminated soil dominated by Pseudomonas sp . served as an inoculum. Phenanthrene mineralization was substantially enhanced upon sorption to mineral-HA complexes and the degree of enhancement was positively correlated with the fraction of sorbed phenanthrene. This stimulation is thought to be related to sorption of both the microorganisms and phenanthrene to the colloidal surfaces. This study suggests that when sorbed contaminants are still bioavailable, the presence of surfaces may stimulate mineralization.

The application of sewage sludge to agricultural soils is practiced to minimize landfill disposal. Organic matter amendments to soil are generally thought to improve soil quality, but pesticide application to these soils may lead to groundwater contamination problems. The complexation of pesticides with a water-soluble carrier such as dissolved organic matter (DOM) may facilitate chemical movement through soil. Sewage sludge amendments may lead to greater downward movement of organic chemicals if associated with DOM. Napropamide [2-α-napthoxy)-N,N-diethylpropionamide] was applied to a silt loam soil with (SS) and without (NoSS) sewage sludge application. Laboratory batch equilibrium and soil column studies were performed to determine the potential for herbicide complexation with DOM. Over 98% of the herbicide in soil columns followed typical adsorption and transport behavior as the center of mass of the lower organic matter soil (NoSS) moved twice the depth as that of SS. However, napropamide was detected in the initial leachate eluted from repacked soil columns with steps taken to prevent preferential flow. Napropamide concentrations in the initial leachate of SS were twice that from NoSS with

Phenanthrene, a three ring aromatic hydrocarbon, was used as a model substrate to distinguish between binding and sorption to dissolved and to mineral-associated humic acid (HA), with an emphasis on its implication to bioavailability. Binding was analyzed by a fluorescence quenching technique using Aldrich HA and HAs derived from compost, loamy and clay loamy soils. Measurements were made both in buffered water and in a mineral medium to be used later in a bioavailability study. Sorption of phenanthrene to mineral-associated HA was analyzed in batch experiments. Mineral–HA complexes were prepared with goethite, hematite, and Ca2+- and Cu2+-montmorillonite. Interaction of HA with clay minerals was greater at low pH and was dependent on the mineral type. Sorption of phenanthrene to these complexes was substantially higher at lower pH and higher when the HA was associated with montmorillonite rather than goethite or hematite. Binding coefficients (Kb(oc)) obtained for dissolved HA were at least an order of magnitude higher than sorption coefficients (Kp(oc)) obtained for mineral-associated HA. Both binding and sorption coefficient values were substantially higher for Aldrich HA. This work emphasizes the need for a detailed sorption study before conducting well controlled bioavailability experiments.

In 1971, an experiment was conducted in a field containing high amounts of residual DDT (dichlorodiphenyltrichloroethane) to evaluate deep plowing, followed by flooding, with and without organic matter applications, as soil and water management tools to reduce total DDT residues and preferentially degrade the residual DDT to DDD [l,l-dichloro-2,2-bis (p-chlorophenyl) ethane]. The experimental site was revisited in 1994 to determine residual soil concentrations of DDT isomers and their metabolites in soil, soil dust, and the atmosphere. Also, volatilization flux measurements were made to evaluate rates of movement into the atmosphere. Soil concentrations of all DDT isomers and metabolites had decreased in all plots, with p, p'-DDE [1, 1-dichloro2,2-bis (p-chlorophenyl) ethylene] the major component of the total remaining residues (DDTR). The total DDTR residues in the surface 75 cm varied from 10 to 28% of their amounts in 1971. The highest concentrations were found in the deep plowed, unflooded plots with DDTR decreasing from 4 mg kg-’ at 0 to15 cm to 0.3 mg kg-’ at 60 to 75 cm. Deep plowing evidently increased DDT persistence by placing it deeper into the soil profile, which protected it from degradation and volatilization. Concentrations of all isomers were lower in the previously flooded plots. Degrading DDT under reducing conditions brought about by flooding lessened or prevented the formation of DDE in the soil thus ultimately reducing its redistribution into the environment. Significant concentrations of both o,p' and p,p'-DDE and DDT were detected in the atmosphere above the plots. Measurable volatilization fluxes were observed over 48-h periods in February and September. Irrigating the soil with 20 mm water dramatically increased the volatilization flux of all the DDT isomers and metabolites, particularly p,p'-DDE. The finding that DDT isomers continue to volatilize

Movement of pesticides from fields in runoff water and on sediment can degrade surface waters. Research typically found that because of the high water-to-sediment ratio, the total amount of pesticide in water greatly exceeded that associated with sediment. These observations suggested that erosion control would have little effect in reducing pesticide transport from the field. A laboratory study was conducted in a miniature furrow system to determine whether reduction in erosion would contribute to a reduction of napropamide [2-α-naphthoxy)-N,N-diethylpropionamide] transport. Variable erosion was created by polymer addition to the water combined with using variable water flow rates. Bromide was used as a nonsorbing independent tracer. Napropamide transport was linearly related to the amount of fine soil particulates eroded. Bromide transport was independent of the amount of erosion, and the percentage of the applied Br - removed in the runoff was less than that of napropamide. The results indicate that reduction in erosion of fine particulates will result in reduced transport of sorbed pesticides from the field.

This study was conducted to reconcile an apparent inconsistency between the simazine laboratory sorption isotherm data and the field lysimeter transport experiment reported by Poletika et al. (this issue). In this investigation, linear and nonlinear one- and two-stage simazine sorption models were fitted to the sorption and desorption isotherm laboratory data to obtain parameter estimates for use in the transport model. Once obtained, the calibrated sorption model was combined with the parameterized outflow concentration record from a mobile Br tracer to represent rate-limited sorption and transport of the simazine added simultaneously with the Br. The calibrated model did an excellent job of representing the final simazine profile in the soil, particularly with the nonlinear model. This is in contrast to a single-stage adsorption model tested by Poletika et al. (this issue), which reached poor agreement with the field profile when laboratory-measured sorption parameters were used. The results demonstrate the compatibility of field and laboratory experiments on pesticide movement and also indicate that sorption isotherms may require substantially longer to reach equilibrium than is customarily allowed in current protocols.

The fumigant 1,3-dichloropropene (1,3-D) has been identified as a partial replacement for methyl bromide (CH 3 Br) in soil fumigation. 1,3-Dichloropropene is formulated for soil fumigation as Telone II (Dow AgroSciences, Indianapolis, IN) for shank application and as an emulsifiable concentrate (EC) (Telone EC or InLine; Dow AgroSciences) for drip application. This study investigated the effect of formulation on the phase partitioning, transformation rate, and volatilization of 1,3-D isomers. Air-water partitioning coefficients (K H ) were slightly higher for Telone II than for Telone EC, presumably due to the higher apparent water solubility of the EC formulation. Sorption of 1,3-D isomers in two soils was not affected by formulation. Formulation had no significant effect on the rate of 1,3-D transformation in water or soil. In general, differences in the rate of 1,3-D transformation and phase partitioning due to formulation as Telone II or Telone EC were very small. Thus, the effect of formulation on 1,3-D fate may be ignored in transformation and phase partition of 1,3-D in water and soil. Packed soil columns without plastic tarp indicated that with relatively shallow subsurface (10 cm) drip application of Telone EC, emission of 1,3-D isomers was more rapid and produced greater maximum instantaneous flux than deeper (30 cm) shank injection of Telone II. Both application methods resulted in the same cumulative emissions for both isomers, 45% for (E)-1,3-D and approximately 50% for (Z)-1,3-D. These results suggest that for drip application of fumigants to be effective in reducing emissions, the fumigant must be applied at sufficient depths to prevent rapid volatilization from the soil surface if the water application rate does not sufficiently restrict vapor diffusion.

Polymer application to soil is a growing practice to improve soil physical properties and reduce soil erosion. Polymer addition can potentially influence herbicide and pesticide sorption in soil. The one-point distribution coefficient K d values of two herbicides in the absence and presence of each of 10 polymers (7 polyacrylamides and 3 polysaccharides) were determined by the batch equilibrium method. The results showed that nonionic napropamide [2-(alpha-naphthoxy)-N,N-diethyl propionamide] sorption was essentially unaffected by the presence of any of the polymers. The influence of polymers on anionic picloram (4-amino-3,5,6-trichloropicolinic acid) sorption depends on the charge characteristics of polymers and salt concentrations in the solution. Electrostatic interaction and competition for sorption sites are two primary underlying mechanisms for the polymer influence. At low salt concentration, the increased picloram sorption in the presence of both cationic and anionic polymers was attributed to different electrostatic interactions and polymer partitioning between soil and solution phases. At high salt levels, the presence of polymers had either no influence or a slightly negative influence on the picloram sorption, which was attributed to competition for sorption sites. In field conditions, it is more likely that polymers have no or a slightly negative influence on herbicide sorption due to the presence of salts.

Polyacrylamide (PAM) treatment of irrigation water is a growing conservation technology in irrigated agriculture in recent years. There is a concern regarding the environmental impact of PAM after its application. The effects of anionic PAM on the sorption characteristics of four widely used herbicides (metolachlor, atrazine, 2,4-D, and picloram) on two natural soils were assessed in batch equilibrium experiments. Results showed that PAM treatment kinetically reduced the sorption rate of all herbicides, possibly due to the slower diffusion of herbicide molecules into interior sorption sites of soil particles that were covered and/or cemented together by PAM. The equilibrium sorption and desorption amounts of nonionic herbicides (metolachlor and atrazine) were essentially unaffected by anionic PAM, even under a high PAM application rate, while the sorption amounts of anionic herbicides (2,4-D and picloram) were slightly decreased and their desorption amounts increased little. The impact mechanisms of PAM were related to the molecular characteristics of PAM and herbicides. The negative effects of PAM on the sorption of anionic herbicides are possibly caused by the enhancement of electrostatic repulsion by presorbed anionic PAM and competition for sorption sites. However, steric hindrance of the large PAM molecule weakens its influence on herbicide sorption on interior sorption sites of soil particles, which probably leads to the small interference on herbicide sorption, even under high application rates.

Experimental evidence supporting the environmental screening model of Jury et al. (1983) is reviewed and discussed. For several laboratory studies of volatilization, initial and boundary conditions matched those used in our model and simulations were run. In all cases, good agreement was found between predicted and measured volatilization losses, with and without accompanying water evaporation. When five chemicals of widely differing volatility were exposed to identical experimental conditions, the model correctly predicted the relative loss behavior observed. The convective mobility predictions of the model were shown to be consistent with several laboratory studies of compound leaching, as long as the water flow rate was slow enough (< 0.01 cm/s) to ensure equilibrium between the solution and adsorbed phases. The Millington and Quirk tortuosity model used in our representation of the soil diffusion coefficient was found to give a good prediction of the water content dependence of the effective diffusion coefficient observed in several studies. The thickness of the stagnant boundary layer predicted from our similarity assumption was shown to be consistent with the apparent thickness inferred from several laboratory and field measurements of volatilization.

Le modele d'etude du transport de composes organiques separe les composes chimiques en categories de volatilisation et mobilite

Thin clay films prepared from aqueous suspensions of the potassium or sodium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) with AI-, Fe-, or Cu-saturated montmorillonite or with montmoril- lonite coated with hydrous oxides of AI, Fe, or Cu were examined in an air-dry condition by infrared (IR) techniques to elucidate possible modes of interaction between picloram and the mineral surfaces. Deuter- ation was used to confirm band assignments of picloram and its salts prior to interaction with montmoril- lonite. Picloram interactions with AI- and Fe-saturated montmorillonite and with montmorillonite coated with hydrous oxides of A1 and Fe were concentration dependent. At high picloram concentrations simi- larities with the IR spectrum of potassium picloram indicated that much of the picloram was present in the salt form. As the concentration of picloram was reduced below that equivalent to 1 meq/g clay, the IR spectrum indicated the presence of the monomeric acid on the mineral surface. The spectrum of picloram on montmorillonite with a coating of copper hydrous oxide was similar to that of a Cu-picloram complex indicating coordination type bonding. The spectrum of picloram with Cu-saturated montmorillonite did not correspond to any of the other spectra of picloram examined. The interaction of picloram with montmo- rillonite coated with a hydrous oxide coating of Cu and with Cu-saturated montmorillonite were indepen- dent of picloram concentration in the range 2.20-0.44 meq/g clay.

Equilibrium dialysis was used to measure the extent of interaction between dissolved organic matter (DOM) and five nonionic pesticides. The association-dissociation of DOM with the relatively polar, nonionic pesticide napropamide [2-(a-naphthoxy)-N,N-diethylpropionamide], was emphasized in this study. A negative linear correlation was found between the log of the solubility and the log of the association coefficient of these five pesticides with dissolved humic acid derived from peat (peat-DHA) (...)

Freshwater sediments were collected from eight different locations in California to study the influence of sediment properties on the adsorption and desorption of the model herbicide, diuron (3-(3,4-dichlorophenyl)-l,l-dimethylurea). The sediments were characterized to physical and chemical properties using the same methods used for soils. The sediments had a range of organic carbon of 0.91 to 19% and were high in silt and clay. The adsorption of diuron was described by the Freundlich equation. Adsorption at 25 °C expressed as the Freundlich coefficient, k, was positively correlated to the amount of organic carbon present. There was no correlation with total CEC. The desorption of diuron was evaluated by taking the difference between the slopes of the adsorption and desorption isotherms. As the difference between these slopes increased, less diuron was desorbed. These differences were positively correlated to k and organic carbon. Adsorption at temperatures of 5, 25, and 40°C on three sediments indicated that the adsorption of diuron decreased as the temperature increased. tern of a lake, then it would not only be important to study their chemical and physical properties, but also the potential retention or release of pesticides on these sediments. The capacity of lake sediments to adsorb or desorb pesticides is likely to be one of the most important factors which influence the concentration of a pesticide in the lake water. Since sediments are formed and exposed to conditions different from soils, it is important to know if the adsorption of a pesticide would vary with the same physical-chemical properties as for soils. The study was undertaken to determine the extent to which variation of several sediment characteristics, including organic matter, cation exchange capacity, and pH, affects sorption of the model herbicide, diuron (3(3,4-dichlorophenyl)-l,l-dimethylurea). Diuron is nonpolar herbicide of relatively low water solubility. It is used as both a preand postemergence herbicide. Additional Index Words: herbicides, pesticides, water quality, sediment characteristics, organic matter content, apparent heats of adsorption. Peck, D. E., D. L. Corwin, and W. J. Farmer. 1980. Adsorption-desorption of diuron by freshwater sediments. J. Environ. Qual. 9:101106. Although herbicide-soil interactions have been extensively studied, litte attention has been given to herbicide-sediment interactions. There have been some investigations of insecticide adsorption on lake sediment (Lotse et al., 1968; Vieth and Lee, 1971); however, there appears to be a lack of quantitative studies of the adsorption of herbicides on lake sediments. Poinke and Chesters (1973) have reviewed the literature on pesticide-sediment interactions. With the increasing use of herbicides in modern agriculture, it is likely that some will reach water bodies. Once in the water, it becomes important to understand the physical-chemical dynamics of the herbicide and sediment. It has been shown that sediments can play an important role in affecting the concentration of pesticides in a lake. Earlier investigations have shown (Bridges, 1961) that as the concentration of a given pesticide decreases in the water phase, there is a concomitant increase in the pesticide content of the sediment. As discussed by Chesters and Konrad (1971), these sediments may act as reservoirs, being able to recycle pesticides back into the aquatic environment. If lake sediments are considered as part of the life sys’ Contribution of the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521. The research leading to this report was supported by the Univ. of California, Water Resour. Center, as part of Water Resour. Center Project UCAL-WRC-W-485. Received 23 Sept. 1978. 2 Graduate Research Assistant, Graduate Research Assistant, and Associate Professor of Soil Science, Univ. of California, Riverside, respectively. Current address of senior author: Cooperative Extension Service, Univ. of Nevada, P.O. Box 651, Overton, NV 89040. Senior author is presently Soil and Water Scientist, Univ. of Nevada Agricultural Experiment Station, Logandale, NV 89021. MATERIALS AND METHODS The sediments were collected from eight different sites in California. Some of the chemical and physical properties of the sediments are listed in Table 1. The sediments were chosen to represent a number of differing environments and to be high in fine materials and organic matter. The sampling tool used to collect the sediment (Fig. 1) was modification of a tool designed by Barkley (1971). The sediment collection tube consisted of a 60-cm (2A-in) length of PVC pipe, 5 cm in) in diameter, with the circumference of one end beveled to aid penetration into the sediment. As the collection tube was pushed into the sediment, air and water were displaced upward through the tool stem. When the tube was filled with sediment, a rubber stopper was placed in the top of the tool. As the tool was withdrawn from the bottom, a vacuum was created holding the sediment in the tube. The success or failure of collecting a sediment sample depended upon the tool being completely air tight before removing the sediment from the bottom. Sediments were collected in water depths ranging from 0.5 to 4 m. Beyond a 4-m water depth it was difficult to maintain sufficient vacuum to hold the sediment in the tube. A composite sample consisting of 12 to 16 cores, 15 cm in depth, was collected at each site. The 0to 15-cm depth was obtained by sectioning the sediment core after removal from the collection tube. The sediment core slipped easily from the collection tube after releasing the vacuum. Intact 60-cm cores were retained in extra collection tubes for additional studies to be reported another time. Once collected, the sediments were immediately quickfrozen in dry ice. The frozen sediments were freeze-dried and each sampling site cornposited and ground to 60-mesh (0.25 mm). Preliminary investigations showed it necessary to reduce particle size to 60-mesh to provide a reproducible, homogeneous sample for the adsorption measurements. Preliminary screening through a 1-mm mesh removed fresh, undecomposed organic matter. Grinding may be expected to have an effect on the final particle size distribution in the sand fraction but would not be expected to significantly affect adsorption properties of the sediments. Most of the adsorption would be expected to be associated with the smaller size fractions. The chemical and physical properties of the sediments were determined using methods developed for soils. Organic carbon was determined using a programmed microcombustion apparatus in a pure oxygen atmosphere (Allison, 1965). In this method any sediments containing carbonates were treated with sulfurous acid before determining carbon. Total N was determined by the semimicro-Kjeldahl method (Bremner, 1965). The percent LOI (loss on ignition) was determined using a procedure developed for ash content (Sneddon et al., 1971) in which the sample was ignited 375°C for 16 hours. Cation exchange capacity of the sediment was determined using a modified BaCl2 method (Chapman and Pratt, 1961). J. Environ. Qual., Vol. 9, no. 1, 1980 101 Published January, 1980

Tests sur 35 composes chimiques selectionnes pour determiner la mobilite convective et diffusive, la susceptibilite a la volatilisation a la surface du sol et la persistance dans le sol en fonction de la profondeur d'incorporation

Dissolved organic matter (DOM) can affect the distribution of solutes between solution and sorbed phases and the availability and environmental fate of the solutes. Batch sorption isotherm techniques were used to evaluate solute-solute and solute-sorbent interactions that control the effects of DOM on the sorption of a nonionic, moderately polar organic solute by solid sorbents. The sorption of napropamide (2-(α-naphthoxy-N,N-diethyl propionamide) by Na⁺-, Cu²⁺-, and Al³⁺-montmorillonite decreased when dissolved humic acid derived from peat (peat-DHA) was present in the slurry. For Na-montmorillonite, the effect of DOM on sorption was reduced when a dialysis membrane prevented contact between the DOM and the clay. This suggests that competition for sorption sites on the clay between DOM and the pesticide contributed to decreased napropamide sorption. The extent of the DOM effect was also dependent on the concentration and the source of DOM added. In contrast to the montmorillonite system, the effect of DOM on napropamide sorption by soil was observed only when the dialysis membrane was present or when the dissolution of native organic matter from the sorbate surface itself was enhanced by increasing the pH of the slurry system. These results demonstrate that the effect of DOM on the sorption of nonionic pesticides by soils and sediments can be a function of the association of DOM with pesticides in the solution phase, interactive forces of both DOM and the pesticide with the sorbent surface and the nature of the sorbent surface. Contribution from the Dep. of Soil and Environ. Sci., Univ. of California, Riverside.